1. Field of the Invention
The present invention relates to a method of correcting a mask pattern which causes a mask pattern of a photomask used when producing a semiconductor device etc. to deform so as to give a transfer image close to a desired design pattern, a correction apparatus working this method of correction, a photomask obtained by this method of correction, an exposure method for performing exposure using a photomask having such a corrected mask pattern, a semiconductor device produced by photo-lithography using a photomask having such a corrected mask pattern, and an apparatus for production of a photomask and an apparatus for production of a semiconductor device using this method of correction.
2. Description of the Related Art
In the production of a semiconductor device etc., the process for transferring a mask pattern to a resist material on a semiconductor wafer is referred to as the photo-lithographic process.
In recent years, along with the increasing miniaturization of the semiconductor devices produced, the design rule has become smaller and lithography is being performed near the theoretical limit of resolution. This fact is leading to the disadvantages of a deterioration of the performance of the semiconductor device due to deformation of the transfer pattern and reduction of yield due to bridging (error connection) and disconnection of the patterns. Accordingly, the mask patterns have been optimized by trial and error so as to obtain the desired resist pattern. The practice has been to prepare mask patterns to which have been added a plurality of modification patterns for a design pattern, find the transfer patterns by simulation in transfer experiments, and add the modification pattern giving the transfer pattern closest to the design pattern to the mask pattern.
In recent years, light proximity effect correction techniques by which mask patterns have been automatically optimized by computer, have been developed. In the light proximity effect correction, the mask pattern deformed so as to improve the transfer image to match with the input design pattern has been sought by computations.
However, it suffers from the following disadvantages in the related art. In the trial and error method, it takes tremendous time and work to find the optimal mask pattern. Therefore, this can only be used for limited patterns. Accordingly, it cannot be used for irregular patterns such as ASICs(Applied Specific Integrated Circuits). Further, in the trial and error method, the number of mask patterns which can be evaluated is limited. Therefore, there is the possibility of overlooking a better mask pattern and the precision of correction of the mask pattern is limited.
Therefore, in recent years, technologies for automatically correcting mask patterns have been developed. These have had the following disadvantages, however.
First, the corrected mask pattern would sometimes cause a deterioration in the processing margin, that is, the exposure margin and the focal depth. Therefore, the correction might conversely cause a deterioration in the yield, making use for actual processes impossible.
Further, one method of correction is to find the distribution of light intensity using simulation of the light intensity, use the contour lines obtained by slicing by the threshold value of the same as the transfer image, and correct this to the optimal mask pattern. In this method, however, no consideration is given to the resist process, so the contour lines obtained by slicing the distribution of light intensity do not match the resist image obtained by the actual process and thus the resist image is not sufficiently corrected.
Further, depending on the method of correction, due to the excessive correction of the corners of the pattern or the ends of the line patterns etc., distortion would occur at other portions, bridging (miss-connection) of the resist pattern would occur when the amount of exposure or focal position fluctuated, or mask patterns difficult to fabricate would be produced.